This invention relates to gun ammunition and particularly to methods for the manufacture of projectiles for gun ammunition and to the projectiles produced thereby. In particular, the method and the projectiles of the present invention relate to ammunition for small-bore weapons of 0.50 caliber or smaller bore and to the use of mixtures of metal powders in the manufacture of projectiles.
The use of a mixture of a heavy metal powder, i.e., a metal having a density greater than the density of lead and a light metal powder, i.e., a metal having a density less than the density of lead, to form a unitary projectile has been suggested. These unitary projectiles, however, suffer several shortcomings. For example these projectiles are almost universally formed by initial compaction in a die cavity. As a consequence, these unitary projectiles are limited with respect to the total weight of a projectile that can be formed in a given cavity. For example, cold-pressed heavy metal powders can be reduced in volume, e.g. densified, by only a limited amount in a die pressing operation. This limitation is in part attributable to the inherent incompressibility of heavy (dense) metal powders. Further, such powders tend to bridge themselves within the die and effectively halt movement of the punch being used to compress the powder within the die. The use of greater die pressing pressures only serves to more firmly bind the green compact within the die, resulting in its destruction when one attempts to extract the pressed compact from the die cavity. These unitary powder-based projectiles, therefore, are limited to a range of overall density which is solely a function of the percentage of the heavy metal powder employed in the powder mixture.
These physical limitations relating to the relative incompressibility of a heavy metal powder, or a mixture of metal powders in which the heavy metal powder is the dominant powder, has led to the use of various techniques for densifying powder compacts, principally by heat treatments such as sintering or alloying of the powders of the mixture. These techniques, among other things, are cost prohibitive when manufacturing large numbers of projectiles. Moreover, these techniques convert the powders of the projectile to solid bodies which destroys certain beneficial features of non-sintered powders, such as their frangibility which is an important feature in projectiles intended for law enforcement and military activities.
U.S. Pat. No. 5,760,331 discloses a projectile formed from a mixture of heavy and light metal powders. This patent teaches a range of percentages of heavy metal powder to light metal powder, as well as the use of a variety of metal powders, but does not teach adjustability of the overall weight of a projectile for each of the percentages. The projectiles of this patent are unitary in that they comprise a single pressed compact of the mixture of metal powders. The density of these unitary projectiles along their length is not noted to be selectable.
U.S. Pat. No. 5,279,787 exemplifies the prior art efforts to densify a die-formed green compact by sintering and/or alloying techniques.
In U.S. Pat. No. 2,393,648 there is disclosed a stratified projectile which is formed by layering in a die cavity a plurality of layers, each of which comprises a mixture of metal powders which, when heated, form an alloy of a specific toughness or hardness. These layers are progressively tougher or harder from the trailing end of the projectile to the tip of the leading end thereof. By this means, the projectile is said to more readily penetrate armor plate. The projectiles of this patent are not subject to alteration of their overall weight without destroying their designed function.
U.S. Pat. No. 4,716,835 discloses a maneuver ammunition cartridge having a disintegrating projectile. The projectile of this cartridge comprises a thin weak outer covering which ruptures upon the cartridge leaving the barrel of the weapon, due to the spin imparted to the projectile by the rifling of the barrel. The projectile of this patent includes a hollow tapered nose section which is filled with a foam material that serves to resist indentation of the covering during cycling of the cartridge through an automatic or semi-automatic weapon. This nose section of the projectile is separated from a plurality of xe2x80x9cpressedxe2x80x9d metal powder bodies that are stacked within the cylindrical body section of the projectile, in axial alignment with one another and with the longitudinal axis of the projectile. The separation between the foam-filled nose section and the powder bodies-containing cylindrical section of the projectile is defined by a xe2x80x9cstiffening insert made of plasticxe2x80x9d and comprises two cup sections each open at one end, and presents a circular disc member oriented transverse of the longitudinal axis of the projectile. Once the outer covering is ruptured by reason of the spin of the projectile after it leaves the gun barrel, all of the components of the projectile dissipate over a short distance so as to not present a danger to troops. This projectile, is useless as a projectile which is intended to strike a target and impart substantial destructive force to the target.
It is an object of the present invention to provide a method for the manufacture of a gun ammunition projectile and by which the overall weight of the projectile and other desirable physical characteristics of the projectile and/or its terminal ballistics are attainable.
It is another object of the present invention to provide a projectile for gun ammunition wherein various physical characteristics, and accompanying performance characteristics, of the projectile are provided.